Motor-assisted variable geometry turbocharging system

ABSTRACT

The motor-assisted variable geometry turbocharging system has a motor to add power to the turbocharging shaft, especially at low exhaust gas volume. Additionally, the turbocharger has control over compressor air inlet direction and/or control of exhaust gas to a two-volute expander. These are individually controlled directly or indirectly from an engine controller to enhance turbocharger performance. In a preferred embodiment, the motor is an electric motor, mounted directly on the turbocharger shaft intermediate the turbo expander and turbo compressor and within the main housing.

FIELD OF THE INVENTION

The present invention relates generally to variable geometry componentsused in turbochargers applied to internal combustion engines thatoperate over a broad range of speed and load.

BACKGROUND OF THE INVENTION

Fixed geometry turbochargers can be designed to operate efficiently at aparticular engine load and speed. However, when operated over a broadrange of engine speed and load, the compressor and turbine componentsare forced to function off their design points and consequently sufferlosses in efficiency that affects engine performance adversely. If theturbocharger is matched to an engine at the engine's rated speed, itwill run considerably off its maximum efficiency where the engine is"torqued down" to low engine operating speeds. Conversely, if theturbocharger is matched to an engine's low speed range, the turbochargerwill have a tendency to "overspeed" when the engine is operated atmaximum speed and load.

To prevent overspeeding in turbochargers that have been matched to thelow engine speed range, a waste gate is frequently used to bypassexhaust gas around the turbine to limit turbine speed over the highengine speed range. The waste gate, however, allows the escape ofexhaust gas energy, which could be better utilized by the turbochargerturbine and results in a substantial loss in system efficiency.

A more efficient system generally known in the trade is one comprisingvariable geometry components in the turbocharger compressor, theturbocharger turbine, or both. The most common types are variable nozzlevanes ahead of the turbine wheel and/or variable diffuser vanes in thecompressor component.

Variable nozzle vanes ahead of the turbine wheel are connected togetherso that the throat area of each nozzle passage can be reduced over thelow engine speed range and increased as the engine speed approaches itsmaximum, so that the turbocharger speed is kept within a safe operatingrange. The positioning of the vanes must be precisely controlled byengine speed and load, and they must be freely movable in the hotexhaust gas environment with minimal leakage through clearance spaces.

The various movable devices that have been employed in the turbochargerturbine have been complicated, expensive, and subject to questionabledurability. Consequently, they have met with limited commercial success.

A more practical approach to a variable device in the engine exhaustsystem was disclosed in U.S. Pat. No. 3,557,549 to Webster, assigned toCaterpillar Tractor Co., 1971. This system employs a flapper valve sopositioned in a divided manifold system that it resides in a neutralposition at high engine speed and load, but can be moved to a secondposition where it diverts all engine exhaust gas flow into one passageof a divided turbine casing at low engine speeds. This essentiallydoubles the flow of exhaust gas through the single turbine casingpassage and maintains the turbocharger speed at higher levels thanotherwise could be reached at low engine speeds. This device is muchsimpler than the complicated variable nozzle vane systems and does notrequire a precise control system for positioning.

The use of the flapper valve to divert exhaust gas allows theturbocharger to be matched efficiently to the higher engine speeds wherethe flapper is in a neutral position. When the engine is operated at lowengine speeds, the diversion of full exhaust flow to the single turbinecasing passage ahead of the turbine increases the turbocharger rotorspeed to provide higher boost pressure to the engine cylinders, allowingthe engine to produce more power and torque than otherwise could beobtained.

The increase in boost at low engine speeds produced by the divertedflapper valve might be great enough to cause the turbocharger compressorto operate in its surge or unstable area. In this case, the compressormust be rematched to move its surge line to lower air flow so that theengine operating points fall within its stable operating regime.However, this causes a movement of the compressor efficiency islands andchoke area to lower flow and can result in lowering the compressorefficiency when the engine is operating at high speed and load.

A variable geometry compressor that can shift the performance map of thecompressor to a lower or higher flow range is one solution to theproblem of keeping the compressor out of surge at low engine speeds andstill maintain high efficiency at high engine speeds. Variable diffuservanes is one type of variable geometry compressor that could beemployed, but the movable vanes cause significant mechanicalcomplication internally in the construction of the turbocharger and mustbe precisely positioned by a rather elaborate control system.

A more practical type of variable geometry device is to employ movablepre-whirl vanes upstream of the compressor wheel to provide positive andnegative pre-whirl to the air entering the inducer of the compressorwheel. Negative pre-whirl moves the compressor operating range to higherflow and usually improves compressor efficiency. Positive pre-whirlmoves the compressor operating vane to lower flow and usually lowerscompressor efficiency somewhat. However, since the maximum island ofcompressor efficiency is also moved to lower flow, the net effect ofpositive pre-whirl is to raise the level of efficiency available to theoperating area of the engine.

It is thus advantageous to connect the movable flapper valve in theexhaust stream to the movable prewhirl vanes in the air stream by amechanical linkage causing them to move in synchronization. With theflapper in neutral, the pre-whirl vanes are positioned to providenegative pre-whirl to the compressor, moving its flow range so thatmaximum efficiency is available in the high engine speed range. When theflapper is in the diverted position, the pre-whirl vanes are moved tothe positive pre-whirl position, thereby moving the maximum compressorefficiency to the low engine speed range. A simple, hydraulic cylindercan be employed as a control means to move the mechanical linkage toeither the high flow or low flow position by sensing the engine speed atwhich the transition is required to be made.

Both the flapper valve and the pre-whirl vanes are external from theturbocharger construction, resulting in much lower overall cost thanother devices that must be built into the internal construction of theturbocharger.

The movement of the compressor flow range by utilizing positive andnegative pre-whirl is more fully described in a paper published in theProceedings of the Institute of Mechanical Engineers, Vol. 18943/75,titled "Experimental and Theoretical Performance of a Radial FlowTurbocharger Compressor with Inlet Pre-whirl," by Wallace, Whitfield andAtkey. It is also described in U.S. Pat. No. 5,025,629 to Woollenweber,June 1991.

At very low engine speed, for example, at low idle, there isinsufficient exhaust gas energy to drive turbocharger fast enough toproduce significant levels of boost. Consequently, there is anappreciable lag time between opening of the engine throttle and when theturbocharger is running fast enough to produce enough boost pressure toeliminate smoke on acceleration, for example. Fuel control devices, suchas rack limiters or aneroid controls, are employed to limit the amountof fuel delivered to the engine cylinders until the turbocharger iscapable of delivering sufficient air to produce smoke-free combustion.These fuel limiting devices cause slower response to throttle openingand a sluggishness in engine and vehicle response.

SUMMARY OF THE INVENTION

In order to aid in the understanding of this invention, it can be statedin essentially summary form that it is directed to a motor-assistedvariable geometry turbocharging system. The variable geometry isprovided by the exhaust gas flow configuration into the exhaust gasturbine and/or the air inlet flow into the air compressor, together witha motor drive for both the turbine and compressor to enhance performanceof a variable geometry turbocharging system.

It is thus a purpose and advantage of this invention to provide a motordrive for the turbo expander shaft to supply power into the turbochargersystem in addition to that which can be achieved by extraction from theexhaust gas, even with a two-volute turbo expander to enhanceperformance, especially at low exhaust gas flow rates.

It is a further purpose and advantage of this invention to provide amotor for adding power to a turbocharger which also includes control ofthe air inlet to the turbo compressor, to enhance performance of theturbocharger even when it is equipped with prewhirl vanes upstream ofthe compressor wheel which controls the rotation of the air as it entersthe inducer of the compressor wheel, to enhance performance of suchsystems by providing the power necessary to provide adequate pre-whirleven at low exhaust gas flow rates.

It is a further purpose and advantage of this invention to supply powerto a turbocharger which is driven by exhaust gas expansion by includinga motor to supply torque to aid in rotating the shaft in the samedirection as exhaust gas expansion, and to include such a turbochargingmotor together with control of air flow into the turbo compressor toenhance vehicle performance.

It is a further purpose and advantage of this invention to provide amotor connected to a turbo compressor shaft and control the motor inaddition to controlling exhaust gas flow to the turbine and/or air flowinto the turbo compressor to enhance engine performance.

It is a further purpose and advantage of this invention to provide anelectric motor, mounted directly on the turbocharger shaft intermediatethe turbo expander and turbo compressor and within the main housing, sothat the above-described purposes and advantages can be attained withminimum space utilization and as an item of original equipment for thevehicle manufacture.

The features of the present invention which are believed to be novel areset forth with particularity in the appended claims. The presentinvention, both as to its organization and manner of operation, togetherwith further objects and advantages thereof, may be best understood byreference to the following description, taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a turbocharging system which has a motorto add power to the shaft, and has control of exhaust gas into atwo-volute turbo expander, with both the motor and the exhaust gas beingcontrolled by an engine controller.

FIG. 2 is a similar view wherein the turbocharger has a motor to helppower the shaft and has control of air into the compressor with controlof both being accomplished from the engine controller.

FIG. 3 is a schematic diagram similar to FIG. 1, together withrotational control of air into the turbo compressor, with all threebeing controlled by the engine controller.

FIG. 4 is a schematic system similar to FIG. 3, but the exhaust gasinlet to the turbo expander is controlled by the engine controller withseparate control of the control of the air inlet to the turbocompressors the motor and separate

FIG. 5 is similar to FIG. 3, but the exhaust gas control and air inletcontrol are controlled together and the motor control is separate.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

To improve engine and vehicle response to opening of the throttle, anexternal power source is needed to operate the turbocharger at higherspeed at engine idle in order to provide increased boost levels in theengine intake system in preparation for quick acceleration. Thisexternal power source can be any convenient rotating power source, suchas an electric motor, a hydraulic motor, a pneumatic motor, or the like,and particularly a motor which can have its power output controlled. Apreferred example and the example given below of an external powersource is an electric motor that engages the turbocharger rotor atengine idle and increases the idle speed of rotation of the rotatingassembly.

Having higher boost pressure available at engine idle speed than theboost pressure the turbocharger can provide from exhaust gas energyalone, allows fuel to be injected into the engine cylinders soonerduring acceleration and reduces smoke and emissions during the transientperiod. The engine is able to produce more output torque duringtransients, and the higher boost pressure during acceleration shouldeliminate the need for fuel limiting devices, such as the aneroidcontrol referred to previously.

The electric motor, coupled to the turbocharger rotor, can be energizedbefore the engine is started. Then, during cranking of the engine, apositive differential pressure will exist across the engine from intakemanifold to exhaust manifold. In the case of a two-cycle engine, apositive differential is necessary for scavenging the cylinder duringcranking. Therefore, if a two-cycle engine is turbocharged with anelectric motor assist the need for a gear-driven blower to provide thescavenge differential pressure needed for starting is eliminated.

The motor-assisted variable geometry turbocharging system of thisinvention is generally indicated at 10 in FIG. 1. Diesel engine 12 hastwo exhaust manifolds 14 and 16 which are separately ducted to the twovolutes 18 and 20 of exhaust gas turbine 22. Valve 24 controls whetheror not exhaust gas is delivered to one or both volutes. When exhaust gasvolume is low, delivery to one volute provides a higher exhaust gaspressure, which delivers more power to the exhaust gas turbine rotor 26.Valve 24 is controlled by valve controller 28, which responds to signalsfrom the engine controller 30. Various signals are fed, into the enginecontroller, such as engine demand and current engine operatingconditions, so that the valve 24 can be appropriately set. The output ofthe engine controlled includes fuel inlet control in addition to the airinlet control in accordance with this invention.

The exhaust gas turbine rotor 26 is mounted on turbocharger shaft 32which, in turn, drives turbo compressor 34. The turbo compressor has acompressor rotor 36 therein so that, when rotated, air is drawn intoinlet 38 and is delivered to outlet 40 to the engine intake system.

This structure is generally seen in Woollenweber U.S. Pat. No.5,025,629, the entire disclosure of which is incorporated herein by thisreference, see FIG. 9 thereof. For the reasons discussed above and inaddition to the variable geometry discussed in that patent, there areproblems in delivering enough combustion air to the engine 12,particularly at low exhaust gas rates. For this reason, motor 42 isattached to rotate turbocharger shaft 32 in the turbocharging direction.The motor 42 may be an electric motor, a pneumatic motor, a hydraulicmotor or other type of motor, providing it can be controlled.Preferably, however, motor 42 is an electric motor, with its rotormounted on shaft 32 and its stator mounted on the interior of theturbocharger housing, with electric control line 45 supplying theappropriate motor control signals. Motor controller 44 is connected tobe managed by engine controller 30. The engine controller 30 preferablyis part of the vehicle engine management system and manages the valvecontrol and motor control for optimum operation of the system to deliverthe optimum amount of combustion air to the engine in accordance withengine demand and current engine operating conditions. When the engineis operating at low speed and there is an engine demand for more powerand more speed, the valve 24 is in the single-volute position and themotor 42 is energized to add power to the turbocharger. As the exhaustgas volume goes up, the valve can be switched to the double-voluteposition and, when exhaust gas is fully adequate to supply the entirepower demand of the turbo compressor, no power need be supplied to themotor 42. If the motor 42 is configured so that it cannot be rotated asfast as the top speeds of the shaft 42, the motor 42 can be disconnectedvia control line 45. Thus, power is supplied to the motor 42 and thevalve 24 is appropriately controlled for optimum turbocharger operatingconditions under the engine speed and demand requirements.

FIG. 2 illustrates a similar turbocharging system 46 for a dieselengine. Turbocharging system 48 has an exhaust gas turbo expander rotor50 mounted on turbocharger shaft 52. Compressor rotor 54 is driven bythe shaft 52 and is mounted in compressor housing 56. Air is deliveredfrom outlet 58 to the air inlet of the engine. Electric motor 60, asdescribed with respect to motor 42, is controlled by a motor controller62 via line 63 which, in turn, is managed by engine controller 64. Theengine controller receives engine demand signals as well as currentengine operating condition signals. From those signals, motor control 62receives appropriate signals to supply power to motor 60 to dive theshaft 52 in the compressor rotation direction. Additionally, the inlet66 of the turbocharger has adjustable vanes such as at 67 therein whichprovide pre-whirl to the inlet stream. As discussed in the referencesabove, this pre-whirl enhances the compressor performance. The pre-whirlcan be adjusted by appropriate adjustment of the vanes which cause thepre-whirl to adjust compressor performance. The vane control 68 thusprovides variable geometry in the turbo compressor. Both the vanecontrol 68 and the motor control 62 are managed from the enginecontroller 64. Each is individually adjusted to provide optimumturbocharging performance under the particular engine operatingparameters and performance demands. The adjustment of turbo compressorconditions by control of input pre-whirl is discussed in theabove-referenced publication.

FIG. 3 shows a turbocharging system 70 similar to the system shown inFIGS. 1 and 2. The turbocharging system 70 has a dual volute exhaust gasexpander with the diverter valve 71, which diverts all exhaust gas flowfrom the split manifold of the engine to one volute for higherperformance at low exhaust gas flow rates, as previously described.Furthermore, the compressor 72 has a pre-whirl control 74 at the airinlet to the compressor 72. Additionally, motor 76 is directly connectedto the turbocharging system main shaft 77 to drive it in the compressordirection. The pre-whirl vane control 78 and the motor control 80respectively control the pre-whirl vanes and the motor 76 but, as FIG. 3illustrates, they are coordinated with each other to optimizecooperative turbocharger air outlet under the existing conditions. Thiscoordination is also present in the valve control 28 with respect tomotor control 44 in FIG. 1 and is also present with respect to the vanecontrol 68 and motor control 62 in FIG. 2. The vane control 78 and motorcontrol 80 of FIG. 3 are both energized by signals from the enginecontroller 82, which includes demand as well as operating parameters.Contrasted to this, the valve control 83 is operated directly from thesignals available in the engine controller 82. Thus, the motor and thepre-whirl control are synchronized and coordinated, while the divertervalve 71 is independently controlled from the valve controller 83.

FIG. 4 shows a system 84 which is structurally much like the system ofFIG. 3. In the controlling of the turbocharging system 84, the enginecontroller 86 provides signals to the motor control 88 which controlsmotor 90 via line 89. Coordinated therewith and cooperating therewith,controller 92 controls through line 93 both the vanes 94 which controlthe pre-whirl and, through line 96, controls diverter valve 97. Sincethe pre-whirl control also controls the diverter valve, the twofunctions are coordinated. Since the motor control is related to thevalve control 92, all of the functions are coordinated and are adjustedin accordance with signals received from the engine controller 86.

FIG. 5 shows a system 98 which is similar to the system 84 of FIG. 4because it has all three of the turbocharging system variables. Thepre-whirl vanes 100 and the diverter valve 102 are both controlled bycontroller 104, which receives its signals from the engine controller106. It is seen that these two variables are cooperative and coordinatedbecause their signal comes from the same controller 104. In this case,however, motor 108 is controlled by motor controller 110, which receivesits signal directly from the engine controller 106. Thus, the pre-whirlvanes and exhaust diverter valve are coordinated and are cooperativelyadjusted. The motor 108 is controlled separately from engine controlsignals.

The motor is sized so that is can contribute torque over a broadoperating range of the turbocharging system. When the engine starts fromidle, the motor is the first and largest contribution to an increase inturbocharger output. The motor remains contributing torque until theexhaust gas, in combination with the turbo compressor inlet control, canprovide adequate air to prevent the engine from running too rich.However, in order to prevent too much boost, as the boost pressure goesup, the motor is turned off before the compressor inlet is controlled toreduce or limit increase in boost.

This invention has been described in its presently contemplated bestmodes, and it is clear that it is susceptible to numerous modifications,modes and embodiments within the ability of those skilled in the art andwithout the exercise of the inventive faculty. Accordingly, the scope ofthis invention is defined by the scope of the following claims.

What is claimed is:
 1. A motor assisted variable geometry turbochargingsystem comprising;a turbo expander for being driven by engine exhaustgas; a turbo compressor for drawing air in an inlet and delivering airunder pressure to the engine, said turbo compressor and turbo expanderbeing connected together to rotate together; air inlet control vanes onsaid compressor air inlet for providing compressor inlet pre-whirl, saidvanes being variable to control the amount of pre-whirl; a vane controlfor controlling said vanes; a motor connected to rotate with saidcompressor to supply power to said compressor to drive said compressorat low exhaust gas flow; a motor control to control said motor, saidmotor control being connected to said vane control so that said motorand said vanes are both controlled by said motor controller; and anengine control responsive to engine conditions, said engine controlbeing connected to said motor control.
 2. The turbocharging system ofclaim 1 further including an exhaust gas inlet valve connected to saidexhaust gas turbine, a valve control for controlling said exhaust gasinlet valve, said valve control being controlled by said engine controland being independent of said motor control and said vane control. 3.The turbocharging system of claim 1 including a turbocharger shaft, saidturbo expander and said turbo compressor being mounted on said shaft,said motor being an electric motor having a rotor mounted on said shaftat a location between said compressor and said expander.
 4. Theturbocharging system of claim 2 including a turbocharger shaft, saidturbo expander and said turbo compressor being mounted on said shaft,said motor being an electric motor having a rotor mounted on said shaftat a location between said compressor and said expander.
 5. Amotor-assisted turbocharging system comprising:an exhaust gas turbinehaving an exhaust gas inlet duct for connection to receive exhaust gasfrom an internal combustion engine, said exhaust gas turbine having arotating turbine wheel therein, said turbine wheel being mounted on ashaft to rotate therewith; a turbo compressor, said shaft extending intosaid turbo compressor, said turbo compressor having an air inlet ductand having a wheel therein mounted to rotate with said shaft to compressair entering said air inlet duct; a motor, said motor being connected tosaid shaft, said motor being energizable to rotate said shaft in anair-compressing direction, motor control means for controlling saidmotor; inlet duct flow control means in at least one of said inlet ductsfor controlling flow therethrough, said inlet duct flow control meansincluding movable pre-whirl vanes in said compressor air inlet duct anda vane control connected to control positions of said movable prewhirlvanes; and engine control means connected for controlling said inletduct flow control means and said engine control means being alsoconnected to said motor control means whereby said engine control meanscontrols said turbocharging system for engine management.
 6. Themotor-assisted turbocharging system of claim 5 wherein said enginecontrol means separately controls said inlet duct flow control means andsaid motor control means.
 7. The motor-assisted turbocharging system ofclaim 6 wherein said exhaust gas turbine is a dual volute turbine andsaid inlet duct flow control means controls exhaust gas flow to one orboth of said volutes.
 8. The motor-assisted turbocharging system ofclaim 5 wherein said inlet duct flow control means includes a valve insaid exhaust gas inlet duct to control exhaust gas flow to said exhaustgas turbine.
 9. The motor-assisted turbocharging system of claim 8wherein said exhaust gas turbine is a dual volute turbine and said inletduct flow control means, when actuated, directs substantially allexhaust gas into one of said volutes to enhance turbine performance. 10.The motor-assisted turbocharging system of claim 9 wherein said motor isan electric motor having its rotor mounted on said shaft at a locationbetween said compressor and said turbine wheel.
 11. A motor-assistedturbocharging system comprising:an exhaust gas turbine having an exhaustgas inlet duct for connection to receive exhaust gas from an internalcombustion engine, said exhaust gas turbine having a rotating turbinewheel therein, said turbine wheel being mounted on a shaft to rotatetherewith; a turbo compressor, said shaft extending into said turbocompressor, said turbo compressor having an air inlet duct aid having awheel therein mounted to rotate with said shaft to compress air enteringsaid air inlet duct; a motor, said motor being connected to said shaft,said motor being energizable to rotate said shaft in an air-compressingdirection, motor control means for controlling said motor; air inletduct air flow control means in said air inlet duct for controlling airflow therein; and engine control means connected to said air inlet ductair flow control means, and said engine control means being alsoconnected to said motor control means whereby said engine control meanscontrols said turbocharging system to deliver adequate air for enginerequirements.
 12. The motor-assisted turbocharging system of claim 11wherein said engine control means separately controls said inlet ductflow control means and said motor control means.
 13. The motor-assistedturbocharging system of claim 11 wherein said engine control meansincludes a valve in said exhaust gas inlet duct to control exhaust gasflow to said exhaust gas turbine.